The present invention relates generally to impeller attachment and more particularly to the attachment of the impeller of plastic material of a coolant pump to the bearing shaft in such a way that the impeller can not rotate with respect to the bearing shaft.
In known attachments, the impeller is attached to the bearing shaft by being pressed onto the shaft, either directly or with a molded insert. This structural scheme presents several problems. For example, almost all plastics tend to swell in coolants. This has resulted in a loosening of the connection between the impeller and the bearing shaft in the previously known designs where plastics have been used, although the changes in dimensions have been in the per thousand range. The loss of strength of the press fit between the impeller and the shaft is caused not only by the swelling of the plastic, but also by the heating of the coolant (and with it of the entire system), since the materials of the bearing shaft and of the impeller have different coefficients of thermal expansion.
The invention is directed to further improving the connection between an impeller made of plastic and the bearing shaft of a coolant pump, especially of the type used in internal combustion engines.